Mine are shot, so my car has no *** up top currently, Is it worth it to rebuild the original carb for the time being?
Or should I leave the original carb alone and wait until the I can pull igntion, swap it for HEI and run a real carb?


Ohh yea, I'm new to the forums but I am a regular on tamparacing.com If anyone has heard of it
-Joe

 

QJet?

If so, the secondaries are rarely "shot." There's usually one simple thing holding them up. Often it is the secondary lockout arm from the choke linkage on the pass. side- it's got a little kicker that holds the secondary throttles from opening any time the choke is on- even a little bit. If your choke doesn't open FULLY this linkage will never disengage and you'll never have secondary throttle opening. Or it could just be stuck. Other than that linkage, easily visible on the pass, side of the carb, there is NOTHING that could prevent the secondary throttles from opening (other than maybe the throttle shaft is rusted solid). The secondary throttles are mechanically linked with the primary throttle arm on a QJet.

Then up top you need to make sure the air valve doors can open. Engine off, you should be able to push them open with your finger agains the very light tension of the air valve tension spring. Again, there is very little that can prevent these from opening.

Last thing that can hold you up is the vacuum diaphragm on the pass. side. It opens and closes slowly with engine vacuum- it acts like a shock absorber for the secondary air valves so they don't just flop open and cause a bog when you lay into it quickly. Make sure it's functioning properly. Retracts when the engine is started, releases slowly (1-2 seconds) when you shut it off again. If it's bad, replace it.

You can also check to make sure your secondary metering rods are still attached to their hanger (it'll never work right if they're not). You can remove one screw and lifter the hanger and rods right off the top of the carb very easily- it's right in between the secondary air valve doors. If one or both of the rods is not attached to the hanger you fish them out with some needle nose pliers, reattach them to the hanger and reinstall.

 

Yea, the vacuum diaphram doesn't retract when the car is started, just sticks out, that must be the reason. If its bad will it totally stop the secondaries from opening?
I didn't see any linkage on the secondaries going to the primary throttle linkage.
Can you buy just the vacuum diaphram?

 

Yes, you can. They go for about $20. Connect it to the angled vacuum port right next to it with a short length of vacuum hose.

There should be a metal linkage going back to the arm on the secondary air valves. If yours is missing it sounds like somebody messed with your carb- all too common with Qjets becuase most people don't know what they're doing with them. Might want to buy a junkyard carb to swipe this linkage off of- they aren't sold separately. It's easy to install while you're replacing the vacuum canister.

Note, that this particular problem will NOT prevent the secondaries from opening, it'll just cause a nasty bog-then-go when they do.

 

It's actually a Rochester...
And yes there is the metal linkage going from the arm on the secondary air valves. I'll post a motor pic.
I think I am just going to go HEI and use a Edelbrock carb. Which will let me get rid of all the wiring, and I'll do the smog stuff at the same time.
I have noticed, sometimes the secondaries won't open, but sometimes they will and it is a VERY noticeable difference.
**EDIT**

 

Oh, sorry- I thought you were referring to the metal link between the vacuum diaphragm and the secondary air valve arm. Your appears to be in tact. The linkage between the primary throttles and the secondary throttles is on the driver's side of the carb. Work the throttle by hand and you'll see how it happens. Secondary throttles don't open at all until about 1/2 throttle then the linkage catches and starts to open the secondary side throttle arm.

I notice the electrical connector on your choke is kinda banged up (single wire, passenger side, attached to the round choke element). Are you sure you're getting voltage to the choke? It MUST open fully when the engine warms up or you can have problems with the secondary lockout linkage not allowing the secondaries to open. Yes, if the condition is marginal it can be sort of intermittent- sometimes it will allow them to open, sometimes it won't.

 

You're referring to this correct?

If so, I'll just clean up the contacts and make sure the wire isn't cut/clashed anywhere.

 

Are you concluding the secondaries aren't opening because you don't see them open when you blip the throttle in the driveway? Wrong conclusion, because you won't see them open under those conditions.

Your lack of top end power probably has more to do with it being an LG4 than anything to do with the carb. You do have a real carb, and trust me, when properly set up you will have plenty of top end! But, again, "LG4" = "no top end" for a lot of reasons. Lame secondary tuning is one reason that relates to the carb, single snorkle air cleaner is another, and the list relating specifically to LG4 continues with restrictive exhaust and barely-bumps-them-open cam.

Keep looking around this forum for q-jet (it's a Rochester quadrajet, which we often refer to a just "q-jet") tuning tips, read the tech article linked from the thirdgen.org home page, you'll see what makes a difference and what doesn't.

Changing the carb is typically a "doesn't", particularly with regard to capability when properly set up.

 

Well I understand they dont have much top-end, but it literally falls on its face.
No, I wasn't just blipping the throttle in the driveway, the motor has to have load.
Also, the air cleaner is off.
The only reason I say it isn't a real carb is the computer controlled junk.

 

Well, I've changed my approach on the cab right now, mainly my concern is on the idle. I've snugged up the carb bolts, seeing they were a little loose, no difference, No vacuum lines are off. I can't figure it out, bad TPS possibly?

 

That fuel line looks pretty badly kinked right after the 90* bend, where it goes into the carb... maybe that should be fixed? That looks like a pretty nasty fuel restriction to me.

 

That isn't the best way to get sympathy around here. . .

Honestly, you can get great power out of that carb when it's operating properly (see sig). Falling on its face at WOT indicates it is not operating properly, and the computer has nothing to do with it in that mode - it goes open loop, and operates like a mechanical carb. You've got a lot of things to check/tune, and you need to be systematic about it.

You say you don't have any vacuum lines off, and also stated no air cleaner. The circled port goes to the air cleaner and is open, and would cause idle problems like that.

I can't tell for sure which one it is, but it appears you have a temp sensor that isn't hooked up on the thermostat housing.

Is your SES light working? Is it coming on?

 

First of all, sorry I was under the preminition that these carbs were junk, nevermind that.

The car doesn't really fall on its face, the engine just mantains its current rpm.

Yes, there is a temp sensor that is not connected on the thermostat housing.

I must've neglected to mention that. Well, when it is covered (port circled above) there is no difference in idle. I will throw the air cleaner on and hook up that line to see if it helps.

Yes, the SES light is coming on, My brother told me to just bridge the ground and read the codes. I will do that tonight after I install my new master cylinder.

I greatly appreciate all your help, thanks man.
-Joe

 

Quadrajets are only "junk" to two kinds of people... those who don't understand them, and those who are afraid of them once they do, lol. Its one of the most complex carbs ever built, and thats why most people are afraid of them... but it also makes them one of the best carbs out there, for performance, reliability, and economy.

BTW - one of your plugs on the thermostat housing is unplugged... that could be your whole problem right there.

 

I looked around for the other plug on the thermostat housing and couldn't find it. I threw the air cleaner and that vacuum line on and the idle dropped down, but not low enough.
Also, what could be the reason the car tries to keep running after the ignition is switched to off? It will continue to fire about 7-8 more times. Even if the car has been running for less than a minute.

 

Well, I jumped the ALDL connectors and check my codes,

23. Low temperature at manifold air temperature sensor OR Throttle position sensor error

AND

44.Oxygen sensor lean

So code 23 means I have a bad TPS or it just needs to be adjusted?
Code 44 obviously means I am running lean. Code that be due to the faulty TPS?

 

O2 sensor lean usually means the sensor is bad or not connected.

If the coolant temperature sensor is not connected, the ECM will not go to closed loop.

 

So, MAT is referring to one of the temp sensors on my thermostat housing?

 

So do you think that other sensor on my thermostat housing is the reason my idle is so hi?
If not, what do I need to do?
Do I need to adjust the TPS?
Happy thanksgiving guys

-Joe

 

I think MAT refers to TPI cars and TPS to carbed? The CC Qjets don't have MATs as far as I know.

I would connect the temp sensor to the thermostat 1st. My connector is shot and so a couple of days ago it I think it gave me some stumbling problems and tripped a code 15, like 57 said it won't go into closed loop without it and hence won't run quite right.

Then I'd replace the choke connector, mine was shot too. Basically the choke will be stuck on, again won't run quite right and secondaries will stay locked out. I bought one off ebay for a couple of bucks.

The TPS sensor is the 3pin connector on the driver side of the carb. I think people stick paper clips through the connector to read the voltages while its connected? The top wire is 5V supply, the middle is the sensor output voltage and the bottom is ground. At idle it should be set to 0.48V. To adjust it though you need to drill out a plug and get the special tool.

Good luck and let us know how you make out.

Happy Turkey Day

 

Well the Temp Sensor is hooked up on my thermostat housing, there are TWO connectors. My temp gauge works so that is hooked up. I am unaware of what the other connector is for as I am unable to locate a plug for it.
BTW my secondaries do open now, just have the idle problem.

 

Got a quote to rebuild the carb, $120 with me supplying the rebuild kit. Any suggested ones?
Semms like on wednesday, my next day off, I am going to adjust the TPS.

 

Did you reconnect the temp sensor on the thermostat housing as 57kid suggested? (This temp sensor is for the computer. The temp gauge sensor is usually in the driver side head.) If you connected the temp sensor try unplugging the ECM power and see if that trouble code comes back.

Did you check the TPS voltage at the connector?

Another thing you could look at is the hose leading to the MAP sensor, mine was plugged and leaking! It routes from the back of the carb to a plastic module on the driver side firewall next to the brake booster.

Let's see if we can check some of these things out before getting it rebuilt. I know how much I hate to put down $$$ only to find it didn't fix my problem.

 

Well, there are two plugs on the thermostat housing. I cannot find the other plug that goes into there. My temp gauge works fine, so I don't know what that other plug is used for. I know the carb needs a rebuild anyway.
On wednesday, maybe I'll do it today, I'll check the MAP sensor.

Doing anything depends on how I fell when I get home from school today. I have to close tonight at work, so I'll need some rest most likely.

 

As stated above, the temp gage does not use the same sensor as the computer does. The computer uses the 2-wire plug on the thermostat housing.

The other thing on the thermostat housing is a thermal vacuum switch that operates the EFE valve on the passenger side exhaust manifold. Here is a diagram of the vacuum routings https://www.thirdgen.org/forums/atta...se-routing.jpg .

If the coolant temperature sensor (CTS), the electrical one on the thermostat housing, was not connected, that could affect WOT because you won't be getting proper ignition advance. The system really does need to have everything operating properly (the EFE valve isn't a big player, though, as long as it isn't stuck shut) with all sensor inputs telling the computer what it needs to know. Otherwise, trying to fix one thing at a time, or doing things that may not be needed (like a carb rebuild when the O2 sensor isn't working properly) aren't going to get the job done. However, if the TPS is not working (it happens), the carb has to come apart to replace that - it can be adjusted externally, though.

 

Ahhh that the info I was looking for Vad.

Ya know I know a few guys who don't run that vac on the secondaries on purpose for that bog then launch. Its very constant and you can already be well into it before the other guy can hit his, as his ain't gonna bog then launch.